[LLVMdev] How to Load a Value?

Zheng Wang jason.wangz at gmail.com
Thu Apr 8 10:40:26 PDT 2010


I have a problem of generating a load instruction. The LLVM bytecode is:

 %2 = call i32 (...)* @atoi(i8*%1) nounwind
 /*<- Insertpos*/

 %5 = icmp sgt i32 %2, %i.0

Now I have

pb: pointer to the Value object of *%2* of bb1.

Here, I want to generate a load instruction and I did it as:

 new LoadInst(pb, "load_2", InsertPos);

where InsertPos points to the position immediately after "%2 = call
i32 (...)* @atoi(i8*%1) nounwind".

BUT I got a runtime error as:

include/llvm/Support/Casting.h:199: typename llvm::cast_retty<To,
From>::ret_type llvm::cast(const Y&) [with X = llvm::PointerType, Y =
const llvm::Type*]: Assertion `isa<X>(Val) && "cast<Ty>() argument of
incompatible type!"' failed."

This is because LoadInst is implemented as:

LoadInst::LoadInst(Value *Ptr, const Twine &Name, BasicBlock *InsertAE)
  : UnaryInstruction(cast<PointerType>(Ptr->getType())->getElementType(),
                     Load, Ptr, InsertAE)

and pb->getType() is not a "PointerType"!!! WHY? Is it because it is a
function call? In this situation, how can I load %2 assuming it has
been load before.

Can anybody gives me some hints?


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